Electrophotographic copying material containing assistant sensitizers and its manufacturing method

ABSTRACT

An electrophotographic copying material, comprising a support sheet having a front and a reverse side, said reverse side having been given an electroconducting treatment and said front side being impregnated with or directly coated with as assistant sensitizer, said front side further having, on the face of the assistant sensitizer applied on said side, a light-sensitive layer (photoconductive layer) containing an organic photoconductive substance. A method for manufacturing the aforesaid copying material, comprising first applying a solution of an assistant sensitizer onto the front side of a support sheet with its reverse side already having been given an electroconducting treatment, drying the applied assistant sensitizer at a temperature ranging from 60* C. to 100* C, and then forming a light-sensitive layer on the face of the applied assistant sensitizer.

United States Patent Nario Yamaguchi;

Kazuo Tubuko, both of Tokyo, Japan [21 App]. No. 729,228

[22] Filed May 15, 1968 [45] Patented Nov. 16, 1971 72] Inventors [73] Assignee Kabushiki Kaisha Ricoh Tokyo, Japan [32] Priority May 29, I967 [33] Japan [54] ELECTROPHOTOGRAPHIC COPYING MATERIAL CONTAINING ASSISTANT SENSITIZERS AND ITS [56] References Cited UNITED STATES PATENTS 3,232,755 2/1966 l-loegl et a1 96/1 3,283,309 11/1966 Gaynor 340/173 3,295,967 1/1967 Schoenfeld 96/15 3,352,669 1 H1967 Murphy 96/1 .5

Primary ExaminerCharles E. Van Horn Assistant Examiner-M. Wittenberg Attorney-Woodhams, Blanchard and Flynn ABSTRACT: An electrophotographic copying material, comprising a support sheet having a front and a reverse side, said reverse side having been given an electroconducting treatment and said front side being impregnated with or directly coated with as assistant sensitizer, said front side further having, on the face of the assistant sensitizer applied on said side, a light-sensitive layer (photoconductive layer) containing an organic photoconductive substance. A method for manufacturing the aforesaid copying material, comprising first applying a solution of an assistant sensitizer onto the front side of a support sheet with its reverse side already having been given an electroconducting treatment, drying the applied assistant sensitizer at a temperature ranging from 60C. to 100C, and then forming a light-sensitive layer on the face of the applied assistant sensitizer.

PATENTEUunv 16 Ian LIGHT ON CHARGE OF CHARGE 0N m w 2 E 2 Jskzwhou momnm TIME (sec) W/ WW 55 IV 5 A, V M m/ Mw w ELECTROPHOTOGRAPHIC COPYING MATERIAL CONTAINING ASSISTANT SENSITIZERS AND ITS MANUFACTURING METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is related to an electrophotographic copying material having a light-sensitive layer containing an organic photoconductive substance, and also to its manufacturing method.

2. Description of the Prior Art There are a number of known organic photoconductive substances such as poly-N-vinylcarbazole. The majority of them, however, absorb only those light rays which are in the range of ultraviolet rays having wavelengths in the vicinity of 335 mu. Therefore, when it was intended to use them as the organic photoconductive substances of the copying materials which are useful for practical purposes, it was necessary to expand the light absorptive sensitivity of these photoconductive substances over the range of the wavelengths of visible light rays. Also known is the art of increasing the light-sensitivity of these photoconductive substances by adding thereto a sensitizer consisting of a dye and an assistant sensitizer consisting of an acid, a metal halide, a quinone, a ketone or the like. For example, there has been proposed an electrophotographic copying material having a light-sensitive layer containing an assistant sensitizer such as those mentioned above in connection with a sensitizing dye and a photoconductive substance. However, such an electrophotographic copying material as one which is provided with a light-sensitive layer which is a mixture of a photoconductive substance, a sensitizing dye and an assistant sensitizer had the following drawbacks with respect to its manufacture and also to its electrostatic characteristics.

For example, in case a metal halide such as zinc chloride and stannic chloride or an acid such as hydrochloric acid, sulfuric acid and phosphoric acid was used as the assistant sensitizer, the resulting electrophotographic copying material obtained had the drawbacks that the chargeability of its lightsensitive layer which is effected by corona discharge was poor and also that a long time was consumed before a saturated potential was attained. Also, in case an acid such as dichloroacetic acid, trichloroacetic acid and picric acid or an acid anhydride was used, the resulting electrophotographic copying material had the drawbacks that its light-sensitive layer exhibited a marked light fatigue (which is a phenomenon in which the chargeability of the light-sensitive layer deteriorates when exposed to light prior to being impressed with an electric charge) and that this copying material exhibited a poor chargeability also when it was intended to charge this copying material by corona discharge. Furthermore, in case the solution for forming a light-sensitive layer was prepared by dispersing, in a dispersing medium, an aforesaid metal halide together with an organic photoconductive substance, this solution had the drawback, in the aspect of manufacturing copying materials, such that the solution would gel when it was left to stand for a length of time on the order of one whole day and night, causing a great deal of difficulty in the application of the solution onto the surface of the support sheet.

SUMMARY OF THE INVENTION lt is, therefore, the object of the present invention to provide an electrophotographic copying material of the type having a light-sensitive layer containing an aforesaid organic photoconductive substance and which overcomes the drawbacks of the electrophotographic copying material of the prior art, and which has desirable properties, especially a quick chargeability, a high saturated potential and a small light fatigue. More particularly, the present invention is concerned with an electrophotographic copying material which, among all other properties, possesses a markedly improved electrostatic characteristic and which comprises a support sheet with its reverse side having been given an .electroconducting treatment and its front side having been processed in such a way that it is first impregnated or coated with an assistant sensitizer and then a light-sensitive layer containing an organic photoconductive substance is formed on the face of the assistance sensitizer which has been already applied to the front side of the support sheet.

As a result of an extensive research on the various drawbacks of the electrophotographic copying materials of the prior art, it has been discovered by us that the aforesaid drawbacks of the electrophotographic copying materials of the prior art result from the occurrence of the phenomena such that, in case the light-sensitive layer of an electrophotographic copying material is formed by including therein a mixture of a photoconductive substance, a sensitizing dye and an assistant sensitizer, there occurs a reaction between the assistant sensitizer and the sensitizing dye, or between the assistant sensitizer and the photoconductive substance, resulting in the gelation of the layer, or resulting in the formation of such undesirable or harmful products as would cause a deterioration of the light-sensitive property of the photoconductive layer, It has been observed also by us, that the solution which is prepared to form light-sensitive layers which consist of such a mixture as described above would undergo intensive changes due to the lapse of time.

The present invention has been worked out based on the knowledge obtained from the foregoing studies which were conducted by us. More specifically, it has been discovered by us that there is obtained an electrophotographic copying material which eliminates the drawbacks of the electrophotographic copying materials of the prior art, by preparing the copying material in such a way that first an assistant sensitizer is coated on or made to be contained in the front side of a support sheet with its reverse side having been given an electroconducting treatment, and then a light-sensitive layer containing an organic photoconductive substance is provided on the resulting face of the front side which has been already treated with the assistant sensitizer.

The light-sensitive layer of the electrophotographic copying material of the present invention which is thus prepared is in the state that the assistant sensitizer which has been coated on or made to be contained in the support sheet is diffused uniformly into the light-sensitive layer starting from the bottom face toward the upper face of said light-sensitive layer. Therefore, the light-sensitivity of the light-sensitive layer is greater in the portion of the layer closer to the surface of the front side of the support sheet which has been treated already with the assistant sensitizer. As a result, the electrophotographic copying material of the present invention is completely free of the drawbacks which have been encountered in those electrophotographic copying materials of the prior art. In addition, according to the present invention, there is provided an advantage that not only the light-sensitivity of the copying material, but also the electric resistivity of the support sheet can be freely regulated as desired by varying the type and the amount of the assistant sensitiker which is applied onto the support sheet and also by varying the condition under which the applied assistant sensitizer is dried. With respect to the drying condition, for example, it is desirable to conduct the drying operation in such a way that, after an assistant sensitizer has been applied onto the surface of a support sheet, the same is dried at a relatively low temperature ranging from 60 C. to C. In case a light-sensitive layer is provided on theface of the assistant sensitizer coating thus formed on the front side of the support sheet, there are obtained the following advantages that not only the dispersion of the assistant sensitizer into the light-sensitive layer is improved greatly, but also the electroconductivity of the support sheet per se is also improved and further that, as a result, there is acquired an electrophotographic copying material having a desired lightsensitivity and a desired electric resistance. Such remarkable features of the electrophotographic copying material of the present invention are considered to be brought about by the fact that the assistant sensitizer which is contained in the lightsensitive layer is caused to evaporate or sublime at the time said layer is dried and thereby the assistant sensitizer becomes diffused uniformly into the light-sensitive layer; that accordingly, there is produced no area in the light-sensitive layer where the assistant sensitizer is present in an excessive amount locally; and that, as a result, the electric resistance of the lightsensitive layer is retained within a desirable range while, on the other hand, the electroconductivity of the support sheet is improved.

The assistant sensitizers which can be applied to the present invention include, for example, organic carboxylic acidsor'organic sulfonic acids such as monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, tetrachlorophthalic acid, phenylacetic acid, phthalic acid, -methylcoumarinylacetic acid, maleic acid, benzoic acid, cinnamic acid, 4-toluene-sulfonic acid and benzenesulfonic acid; metal halides such as zinc chloride, stannous chloride, stannic chloride, aluminum chloride, nickel chloride, ferrous chloride, cuprous chloride, barium chloride, sodium chloride, calcium chloride, lithium chloride, titanium trichloride, arsenic trichloride, antimony pentachloride, magnesium chloride, magnesium bromide, potassium bromide, calcium iodide, strontium bromide, chromic bromide, manganous chloride, ceric chloride, cerous bromide, mercury chloride and arsenic tri-iodide; boron halides such as boron trifluon'de and boron trichloride; quinones such as benzoquinone (1,4), 2,S-dichlorobenzoquinone, 2,6-dichlorobenzoquinone, chloroanilnaphthoquinone (1,4), 2,3-dichloronaphthoquinone (1,4), anthraquinone, 2methylanthraquinone, 1,4- dimethylanthraquinone, l-chloroanthraquinone, anthraquinone-2-carboxylic acid, l,5-dichloroanthraquinone, l-chloro- 4-nitroanthraquinone, phenaanthraquinone, acenaphthoquinone, pyrananthraquinone, chrysenquinone, thionaphthenequinone, anthraquinone-l ,8-disulfonic acid and 2-anilide-l,4-naphthoquinonesulfonic acid; aldehydes such as bromal, 4-nitrobenzaldehyde, 2,6-dichlorobenzaldehyde, 2- ethoxy-l-naphthaldehyde, oxyindole-3-aldehyde, pyridine- 2,6-aldehyde, biphenyl-4-aldehyde and furfural; ketones such as acetophenone, benzophenone, Z-acetylnaphthalene, benzylbenzoin, S-benzoylacenaphthene, 9-acetylanthracene, 9-benzoylanthracene and acetoacetic anilide; salts such as zinc nitrate, aluminum nitrate, magnesium nitrate, manganese nitrate, sodium formate, magnesium acetate, potassium acetate, potassium tartrate, ammonium citrate, ferric sulfate, zirconium acetate, magnesium sulfate and zinc chromate; halides or nitrides such as styrene bromide, 1,3-dinitrobenzene, l-nitro-2-dichloro-benzene, tricyanobenzene, trinitrobenzene, l-nitro-3,4-dichloro-benzene, -chloro-2- nitroaniline, 2,4,6-trinitroanisole, picryl chloride, tetrabromoxylene, 1,5-dichloronaphthalene, 1,8- dichloronaphthalene, 1,4-dinitronaphthalene, 1,8-dichloronitronaphthalene, 4-nitrodiphenylbenzoic acid, 4,4- dinitrodiphenylbenzoic acid, trinitrobenzoic acid, iodoform, picric acid, tetracyanoethylene and 4-nitroacenaphthene; and inorganic acids such a hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid. The aforesaid assistant sensitizers are used in such a way that they are dissolved in a solvent such as water, methanol and toluol, and the resulting solution is applied onto the front side of a support sheet.

Support sheets which can be applied to the present invention include tracing paper, high quality paper, art paper, baryta paper and polyester film, all of which have been given an ordinary electroconducting treatment on their reverse sides. In case a metal plate is employed as the support sheet, the plate after having been processed according to the procedure of the present invention will serve as a printing plate.

Organic photoconductive substances which can be applied to the present invention include the following compounds containing heterocycle and condensed ring, such as: poly-N- vinyl-carbazole, poly-N-dimethylaminoacenaphthylene poly- N-vinylnitrocarbazole, poly-N-dimethylaminocarbazole, polyvinyl anthracene, polyvinyl nitronaphthalene and their polymers.

Sensitizing dyes which can be applied to the present invention include Rhodamine G, Rhodamine B, Rhodamine S, Methyl Violet, Ethyl Violet, Crystal Violet, Methylene Blue FZ, Methylene Blue BH conc., Victoria Blue B, Brilliant Green GX, Malachite Green, Auramine G conc. and Acridine Orange NS.

The electrophotographic copying material which is prepared by the use of the aforementioned constituent materials and in such a way that an aforesaid assistant sensitizer and a light-sensitive layer are applied, in separate steps, onto the front side of the support sheet pennits it to be charged quickly by corona discharge and also permits it to be charged to a suffrciently high potential. Accordingly, the electrophotographic copying material of the present invention has a light-sensitivity which is by far superior to that of the conventional electrophotographic copying materials. Besides, the electrophotographic copying material of the present invention is quite easy to manufacture. Moreover, the solution which is prepared according to the present invention and which is applied onto a support sheet is completely free of such a gelling phenomenon as has been seen in the solutions of the prior art, and this fact insures that the solution can be applied uniformly onto the front side of the support sheet. The fact that the solution which is prepared according to the present invention and intended for being applied onto the surface of the support sheet is free of the changes which are caused by the lapse of time, in sures that electrophotographic copying materials having uniform quality and uniform properties can be manufactured. Furthermore, by the combined use, together with an assistant sensitizer, of an electroconductive material, such as polyglycol, a surface active agent or a synthetic resin at the time the support sheet is impregnated with the assistant sensitizer, there is obtained an electrophotographic copying material having a further improved light-sensitivity.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a graph showing the electrostatic characteristic of the electrophotographic copying materials of the present invention and that of the control electrophotographic copying materials.

More specifically, FIG. 1 shows the electrostatic characteristic of the electrophotographic copying materials prepared in the example 4 of the present invention which will be described later, in which the Curve 1 represents the electrostatic characteristic of the copying material of the present invention and the Curve 2 represents that of the control copying materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will hereunder be described in further detail in connection with the preferred embodiments of the present invention.

EXAMPLE I A solution of an assistant sensitizer was prepared by diluting 5 g. of concentrated nitric acid in g. of methanol. This solution was uniformly applied onto the front side of a support sheet consisting of high quality paper with its reverse side having been given an electroconducting treatment (by the use of, for example, surface active agents) so that the front side of the sheet was impregnated uniformly with this solution. The applied solution was dried at 80 C. for 1 minute. Thereafter, a light-sensitive layer was formed on the resulting from side of the support sheet by applying, by relying on the rotary applicztion technique and to a film thickness of 4.0 a solution poly-N-vinylcarbazole (a 5 percent by weight monochlorobenzene solution) onto the face of the Supp sheet already coated with said assistant sensitizer. The applied light-sensitive layer was then dried at C. for 5 minutes to regulate the moisture content thereof so as to be 4.0 percent. Thus, electrophotographic copying materials were obtained. For comparison, control electrophotographic copying materials were prepared by applying said solution for forming a lightsensitive layer directly onto the front side, which carries no assistant sensitizer coating, of a support sheet consisting of similar, high quality paper and then drying the same, in a manner similar to that described above in connection with the product of the present invention.

The respective copying materials of these two groups were impressed with a negative charge by corona discharge of 6 KV. Thereafter, the resulting copying materials were exposed for 3 seconds to light rays coming from an incandescent tungsten lamp of 200 inches through an original which was laid thereon and then the exposed copying materials were developed by wet developing process. The result was that well-contrasted images faithfully reproducing the original images were formed on the front sides of the copying materials of the present invention. Whereas, the copied images which were formed on the control copying materials were quite obscure due to the poor light-sensitivity to the visible light rays of the control copying materials, and accordingly these copied images of the control copying materials, and accordingly these copied images of the control copying materials were not usable for practical purposes.

EXAMPLE 2 Onto the face of the assistant sensitizer which was prepared according to the manner described in example 1 and coated on the front side of the high quality paper was applied, by relying on the rotary application technique and to a film thickness of 4.5;; a light-sensitive layer-forming solution which was prepared by adding 1.4 g. of Rhodamine B (a 1 percent by weight methanol solution) to 100 g. of a poly-N-vinylcarbazole solution (a 5 percent 1 weight monochlorobenzene solution). Thereafter, the resulting layer was dried at 120 C. for 5 minutes to regulate the moisture content to 4.5 percent. Thus, electrophotographic copying materials were obtained. Also, control electrophotographic copying materials were prepared by applyingin the same manner as for the copying materials of the present inventionthe aforesaid light-sensitive layer-forming solution directly onto the support sheets which consisted of the high quality paper which was used in example 1, and by drying the same to regulate the moisture content as had been carried out for the copying materials of the present invention.

The faces of the light-sensitive layers of the copying materials of these two groups were impressed with a negative charge and then they were exposed to visible light rays coming from an incandescent lamp, in the same way as described in example 1. It was noted that the copying materials of the present invention exhibited a drop of the potential, or a light decay, of their light-sensitive layers which was about 8 times greater in velocity as compared with the velocity of the light decay of the control copying materials.

EXAMPLE 3 A solution of an assistant sensitizer which was prepared by dissolving 1.0 g. of picric acid in 99 g. of methanol was applied uniformly onto the front side of support sheets consisting of art paper and having their reverse sides given with an electroconducting treatment, said application being performed in such a way that the amount of the assistant sensitizer adhering to said front side was 0.03 g./m and the applied assistant sensitizer was dried at 60 C. for 1 minute thereafter, a poly-N- vinylcarbazole solution (a 5.0 percent by weight monochlorobenzene solution) was applied onto the face of the applied assistant sensitizer so that the thickness of the resulting film was 3.0;1. and thus a light-sensitive layer was formed on each front side of the support sheets. Thereafter, the lightsensitive layers were dried at 120 C. for 2 minutes to regulate the moisture content to 4.0 percent. In this way, electrophotographic copying materials were obtained. For the purpose of comparing the abilities, there were prepared control electrophotographic copying materials by applying the aforesaid light-sensitive layer-forming solution onto the front sides of the support sheets consisting of the same art paper not having an assistant sensitizer applied thereto, and by regulating the moisture content thereof by drying the same, in a manner similar to that employed in the manufacture of the copying materials of the present invention.

The light sensitivity of the copying materials of these two groups was measured. The result was that the copying materials of the present invention were noted to have a light sensitivity in substantially the entire range of the visible light rays, whereas the control copying materials showed a maximum light sensitivity to only those light rays having a wavelength of 355 mu. Also, the copying materials of these two groups were imparted with electrostatic latent images in the manner similar to that described in example 1, and then they were developed by the dry developing process. It was noted that very clear copied images were formed on the surfaces of the copying materials of the present invention, while the copied images formed on the control copying materials were markedly obscure.

EXAMPLE 4 A light-sensitive layer-forming solution which was prepared by adding 1.4 g. of a Methylene Blue FZ solution (a 1.0 percent by weight methanol solution) to g. of a poly-N-vinylcarbazole solution (a 5.0 percent by weight monochlorobenzene solution) was applied, by using the same processed art paper which was prepared in example 3, onto the face of the assistant sensitizer which had been applied onto the front side of said art paper, in such a way that the thickness of the film was 4.0p., by relying on the rotary application technique, and thus a light-sensitive layer was formed on each of the support sheets. Thereafter, the light-sensitive layers were dried at C. for 3 minutes to regulate the moisture content to 4.5 percent, with the result that electrophotographic copying materials were obtained. Also, control elec trophotographic copying materials were prepared by applying the aforesaid light-sensitive layer-forming solution directly onto the front sides of the support sheets consisting of the same art paper used in example 3, and then by regulating the moisture content thereof by driving the same in the same manner as that employed in the manufacture of the copying materials of the present invention.

The electrostatic characteristics of the resulting copying materials of the two measured and compared. The result is shown in FIG. 1. In FIG. 1, the vertical axis is provided with graduations to indicate the surface potential (V) exhibited by the light-sensitive layers of the copying materials of the respective groups when the layers were impressed with a negative charge (charge on) by corona discharge (6 KV) while the horizontal axis is provided with the graduations indicating time (second). FIG. 1 is, therefore, a graph of the electrostatic characteristics of electrophotographic copying materials showing the manner in which the surface potentials of the copying materials of the respective groups change by the cessation of the impression of electric charge (charge off) and by the exposure of the light-sensitive layers to light (light on). In a drawing, Curve 1 represents the electrostatic characteristics of the copying materials of the present invention, whereas Curve 2 represents that of the control copying materials.

As will be noted from FIG. 1, the copying materials of the present invention exhibit a saturated potentialat the time they are impressed with an electric charge-which is about 2 times higher than that exhibited by the control copying materials, and the former exhibit a very quick light decay when exposed to light. When the velocity of the light decay which was exhibited by the copying materials of the present invention was compared with the velocity of the light decay of the control copying materials with respect to the time required by the copying materials of the two groups until their surface potential dropped due to exposure to light (light on) to about A of the potential which the light-sensitive layer had immediately before the exposure the velocity of the light decay of the copying materials of the present invention was noted to be about 12 times greater than that of the control copying materials. This indicates the feature of the copying materials of the present invention that they can be satisfactorily applied to high speed electrophotographic copying.

EXAMPLE An assistant sensitizer solution which was prepared by dissolving 5 g. of zinc chloride in 95 g. of methanol was applied uniformly onto the front side of the support sheets consisting of mat tracing paper with its reverse side having been given an electroconducting treatment, in such a way that the amount of said assistant sensitizer adhering to said front side was 0.] g./m, and the applied assistant sensitizer was dried at 70 C. for 1 minute. Thereafter, a light-sensitive layer-forming solution which was prepared by adding l.0 g. of a Crystal Violet solution (a l percent by weight methanol solution) to 50 g. of a poly-N-dimethylaminoacenaphthylene solution (a 5.0 percent by weight methyl cellosolve solution) was applied onto the face of the applied assistant sensitizer, by the rotary application technique, in such a way that the thickness of the resulting film was 3.5 After light-sensitive layers had been thus formed, the layers were dried at 130 C. for 3 minutes to regulate the moisture content to 4.0 percent, and as a result, electrophotographic copying materials were obtained. For comparison, control electrophotographic copying materials were prepared by applying the same light-sensitive layer-forming solution directly onto the front sides of the support sheets consisting of the same tracing paper not having been previously coated with said assistant sensitizer, and thereafter regulating the moisture content by drying the formed light-sensitive layers. The copying materials of these two groups were compared of their electrostatic characteristics in the same manner as described in example 4. The result was that the copying materials of the present invention showed an intensive building-up of potential when they were impressed with an electric charge, and they also showed a saturated potential which was about 1.5 times higher than that exhibited by the control copying materials, and further, they showed a velocity of light decay which was about times greater than that exhibited by the control copying materials. Moreover, the aforesaid assistant sensitizer solution and said light-sensitive layer-forming solution were mixed together and the resulting mixed solution was left to stand for one whole day and night. At the end of this period, gel-like precipitates were noted to have formed in the mixed solution. An extremely great difficulty was experienced in forming a light-sensitive layer on a support sheet by the use of this mixed solution. Also, the control copying material thus formed showed an electrostatic characteristic which was so markedly poor that this copying material was noted to be unusable for practical purposes.

EXAMPLE 6 An assistant sensitizer solution which was prepared by dissolving 5.0 g. of iodoform and 2.5 g. of Anqurd 12 (the trade name of a surface active agent produced by Lion Armor Company) in 92.5 g. of methanol was applied uniformly onto the front sides of the support sheets made of a polyester film with its reverse side having been given an electroconducting treatment, in such a way that the amount of the assistant sensitizer adhering to the front side was 0.5 g./m followed by drying the same at 90 C. for 1 minute. Thereafter, a light-sensitive layerforming solution which was prepared by adding 1.0 g. of Brilliant Green solution (a 1.0 percent by weight methanol solution) to 100 g. of a poly N-vinylnitrocarbazole solution (a 5.0

percent by weight dimethylformamide solution) was applied onto the face of the applied assistant sensitizer, by the rotary application technique, in such a way that the resulting film had a thickness of 4.5g, to thereby form light-sensitive layers.

Then, the formed light-sensitive la ers were dried at 120 C. for 2 minutes m darkness to regu ate the moisture content,

and thus, electrophotographic copying materials were obtained. For comparison, control electrophotographic copying materials were prepared by applying the same light-sensitive layer-forming solution directly onto the front sides of the support sheets made of said polyester film not having been coated with said assistant sensitizer, and by regulating the moisture content of the formed light-sensitive layers by drying.

The copying materials of these two groups were compared of their electrostatic characteristics in the same manner as that described in example 4. It was noted that'the copying materials of the present invention showed a velocity of light decay which was about 5 times greater than that exhibited by the control copying materials.

What is claimed is: l. A method for manufacturing an electrophotographic copying material which comprises the steps of:

applying onto the front surface of an electrically conductive support sheet a solution consisting essentially of at least one assistant sensitizer selected from the group consisting of organic carboxylic acids, organic sulfonic acids, metal halides, boron halides, quinones, aldehydes, ketones alkali metal salts of inorganic acids, alkali metal salts of organic acids, alkaline earth metal salts of said inorganic and organic acids, ammonium salts of said inorganic and organic acids, organic nitro compounds, organic halides and inorganic acids; drying the applied solution at a temperature ranging from 60 C. to C. thereby forming a coating thereon; and then applying onto the upper surface of said coating a solution consisting essentially of an organic photoconductive substance selected from the group consisting of poly-N-vinylcarbazole, poly-N-dimethylaminoacenaphthylene, poly- N-vinylnitrocarbazole, poly-N-dimethylaminocarbazole, polyvinyl anthracene and polyvinyl nitronaphthalene thereby forming a light-sensitive layer on said surface; and then drying the applied solution at an elevated temperature to cause a portion of the coating to diffuse into said layer.

2. A method according to claim 1, wherein the solution containing said organic photoconductive substance further contains a small amount of sensitizing dye.

3. A method according to claim 2, wherein said sensitizing dye is at least one selected from the group consisting of Rhodarnine G, Rhodarnine B, Rhodamine S, Methyl Violet, Ethyl Violet, Crystal Violet, Methylene Blue FZ, Methylene Blue BH conc., Victoria Blue B, Brilliant Green GX, Malachite Green, Auramine G conc. and Acridine Orange NS.

4. A method according to claim 1, wherein the solution containing said assistant sensitizer further contains a compound selected from the group consisting of polyglycols and surface active agents.

5. A method according to claim 1, wherein the solution containing said assistant sensitizer comprises a solvent which is one selected from the group consisting of water, methanol and toluol.

6. A method according to claim 1, in which said support sheet is selected from the group consisting of paper and polyester film whose reverse side has been given an electroconducting treatment.

7. An electrophotographic copying material made by the process of claim 1.

i i i 1' 

2. A method according to claim 1, wherein the solution containing said organic photoconductive substance further contains a small amount of sensitizing dye.
 3. A method according to claim 2, wherein said sensitizing dye is at least one selected from the group consisting of Rhodamine G, Rhodamine B, Rhodamine S, Methyl Violet, Ethyl Violet, Crystal Violet, Methylene Blue FZ, Methylene Blue BH conc., Victoria Blue B, Brilliant Green GX, Malachite Green, Auramine G conc. and Acridine Orange NS.
 4. A method according to claim 1, wherein the solution containing said assistant sensitizer further contains a compound selected from the group consisting of polyglycols and surface active agents.
 5. A method according to claim 1, wherein the solution containing said assistant sensitizer comprises a solvent which is one selected from the group consisting of water, methanol and toluol.
 6. A method according to claim 1, in which said support sheet is selected from the group consisting of paper and polyester film whose reverse side has been given an electroconducting treatment.
 7. An electrophotographic copying material made by the process of claim
 1. 